This application claims benefit of Japanese Patent Application No. 2001-376722 filed on Dec. 11, 2001, the contents of which are incorporated by the reference.
The present invention relates to radar systems and, more particularly, to radar system having a passive milliwave image receiving function for obtaining image data through receipt of milliwaves from moving or stationary concerned object, as well as related method of obtaining images, control method based on image data and monitoring method using milliwaves.
Person""s bodies or the like are generating milliwaves as well as infrared rays, and it is possible to receive such milliwaves by receiving antennas and utilize the received milliwaves for security systems or the like. Specifically, milliwaves can be utilized for detecting guns and other weapons concealed inside the clothing of person passing through a security gate in an air port for getting on board.
Prior art techniques in or related to such a technical field are disclosed in, for instance, Japanese Patent Laid-Open No. 2000-101903 entitled xe2x80x9cImage Processing System and Method and Recording Mediumxe2x80x9d (hereinafter referred to as first prior art), Japanese Patent Laid-Open No. 2001-99930 entitled xe2x80x9cPeripheral Monitoring Sensorxe2x80x9d (hereinafter referred to as second prior art), Japanese Patent Laid-Open No. 6-331725 entitled xe2x80x9cMilliwave Image Pick-Up Devicexe2x80x9d (hereinafter referred to as third prior art), Japanese Patent Laid-Open No. 9-197042 entitled xe2x80x9cMilliwave Camera Systemxe2x80x9d (hereinafter referred to as fourth prior art), Japanese Patent Laid-Open No. 10-148673 entitled xe2x80x9cMilliwave Imaging Radarxe2x80x9d (hereinafter referred to as fifth prior art), Japanese Patent Laid-Open No. 11-83996 entitled xe2x80x9cMilliwave Detection Systemxe2x80x9d (hereinafter referred to as sixth prior art) and Japanese Patent Laid-Open No. 11-13314 entitled xe2x80x9cMilliwave Image Forming Systemxe2x80x9d (hereinafter referred to as seventh prior art).
The first prior art discloses an image processing technique capable of easily detection of an IC card attached to the breast of a person from a remote position, thus permitting reduction of image processing efforts for recognizing ID data.
The second prior art discloses a monitoring sensor for peripheral sensing, which can reliably sense relative position, relative speed and shape of an object.
The third prior art discloses a milliwave image pick-up device for reducing the output time after realization of securing high accuracy eyesight image.
The fourth prior art discloses a smaller-size, lighter-weight and less inexpensive milliwave camera system than plane antenna techniques using multiple-layer dielectric substrate.
The fifth prior art discloses a milliwave imaging radar capable of accurate imaging of the shape of the object to be detected by suppressing the phenomenon of xe2x80x9cgrintxe2x80x9d in order to solve the problem that with images, which are obtained as a result of transmission of radio waves from a transmitter and imaging the intensity of radio waves reflected from a measurement object to be detected (such as a gun concealed inside clothing), the measurement object becomes different in shape from the original shape due to the phenomenon called xe2x80x9cgrintxe2x80x9d and can no longer be distinguished from other objects, so that such images can not be applied to the field of security such as weapon detection.
The sixth prior art discloses a milliwave detecting system capable of detecting forbidden items concealed inside clothing by utilizing weak milliwaves not harmful to the person""s body.
The seventh prior art discloses a milliwave image forming system based on an FM-CW radar an additional function of judging whether it is in a detection object range by obtaining distance data of an object generated as milliwave images.
In either of the above prior art techniques, however, with frequency increase minute antenna distortions and errors in connection cable due to temperature or like cause are no longer ignorable to disable obtaining highly accurate images.
Accordingly, it is an object of the present invention to provide radar system capable of suppressing adverse effects of minute antenna distortions and errors in connection cables due to temperature or like cause to enable obtaining highly accurate images, as well as related method of obtaining images, control method based on image data and monitoring method using milliwaves.
It is another object of the present invention to provide a radar system, which uses high frequency waves (i.e., milliwaves) in, for instance, 94-GHz band for obtaining clear motion picture images, as well as related method of obtaining image, control method based on image data and monitoring method using milliwaves.
According to an aspect of the present invention, there is provided radar system for displaying images of a person""s body or like concerned object on a monitor or the like by receiving milliwaves emitted from the concerned object comprising: a calibration signal source for generating a milliwave calibration signal at the time of calibration; a receiving antenna having an effectively two-dimensional receiving antenna function; and a signal processor for compensation processing a milliwave received signal from the concerned object received by the receiving antenna based on the calibration signal received by the receiving antenna.
The compensation processing in the signal processor executes phase compensation based on phase relation between the received signal from the concerned object and the calibration signal. The receiving antenna is a two-dimensional plane antenna having a plurality of sub-antennas. The receiving antenna is constituted by two mobile receiving antennas movable in different directions. The radar system further comprises an analog-to-digital converter for converting received signals from the sub-antennas of the effectively two-dimensional receiving antenna in the receiving antenna to digital data, the signal processor including a correlator for obtaining correlations of the digital data and a two-dimensional FFT for executing Fourier transform of the correlations. The the calibration signal has a sufficiently high level compared to milliwaves from the concerned object, the received signals are negligible or attenuated during calibration step.
According to another aspect of the present invention, there is provided a method of obtaining images of person""s body or the like concerned object by obtaining image data thereof by receiving milliwaves emitted therefrom, wherein: received milliwave signal from the concerned object received by a receiving antenna is compensation processed on the basis of a predetermined milliwave calibration signal received by the receiving antenna, which effectively has a two-dimensional receiving antenna function, at the time of calibration, thereby obtaining image data of the concerned object.
The compensation processing executes phase compensation based on phase relation between the received signal from the concerned object and the milliwaves calibration signal. The calibration signal has a sufficiently high level compared to milliwaves from the concerned object, the received signal or signals being negligible or attenuated at the time of the calibration.
According to other aspect of the present invention, there is provided a control method comprising the steps of: compensation processing a milliwave received signal emitted from concerned object and received by a receiving antenna, which effectively has a two-dimensional receiving antenna function, based on a predetermined milliwave calibration signal received at the time of calibration, thereby obtaining image data of the concerned object; and executing predetermined control according to the obtained image data.
The calibration signal has a sufficiently high level compared to milliwaves from the concerned object, the received signal or signals being negligible or attenuated at the time of the calibration.
According to further aspect of the present invention, there is provided a method for monitoring object using milliwaves, wherein received milliwave signal from the concerned object received by a receiving antenna is compensation processed on the basis of a predetermined milliwave calibration signal received by the receiving antenna, which effectively has a two-dimensional receiving antenna function, at the time of calibration, to obtain image data of the concerned object, and the object is monitored based on the obtained image data.
The calibration signal has a sufficiently high level compared to milliwaves from the concerned object, the received signal or signals being negligible or attenuated at the time of the calibration. The concerned object is a person""s body.
Other objects and features will be clarified from the following description with reference to attached drawings.